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Français Passive plant: cables, panels, splices, splitters, filters
Between two transceivers lies the passive plant — everything that carries or joins the light without being powered. It decides most of the link's loss, all of its reflections and nearly all of its faults, and it outlives several generations of the optics plugged into it. This page catalogues the components — cable types and constructions, patch panels and pigtails, fusion and mechanical splices, connectors and adapters, attenuators, PON splitters, WDM filters, enclosures — with their loss allowances and the design and handling rules that keep the budget honest.
Cables
| Type | Construction | Fibre count | Where | Notes |
|---|---|---|---|---|
| Simplex / duplex patch cord | 1–2 fibres, 900 µm tight buffer, 2–3 mm jacket, connectors both ends | 1–2 | rack, module to panel | LC-LC, LC-SC, MPO-MPO; length 0.5–30 m |
| Distribution (indoor) | 900 µm tight-buffered fibres, aramid, LSZH/OFNR/OFNP jacket | 4–144 | building risers, between rooms | terminated on panels or pre-terminated cassettes |
| Breakout / fan-out | each fibre in its own 2 mm sub-cable | 2–24 | direct connectorisation without panels | rugged, bulky |
| Loose tube (outdoor) | 250 µm fibres in gel- or dry-filled tubes around a strength member, water-blocking, PE jacket | 12–288 | ducts, direct burial, aerial | temperature range −40…+70; must be spliced to pigtails indoors |
| Ribbon / rollable ribbon | 12 fibres bonded side by side, mass-spliced | 144–6 912 | high-count backbone, data-centre interconnect | 12-fibre mass fusion splicing |
| Armoured | corrugated steel or FRP layer | any | rodent and crush protection, direct burial | grounding of metallic armour |
| ADSS (all-dielectric self-supporting) | aramid-strength aerial cable | 12–144 | pole lines, power-line rights of way | spans 100–1 000 m |
| OPGW | fibres inside the ground wire of HV lines | 12–96 | utilities | — |
| Micro-cable / air-blown | 200 µm fibres, thin cable blown into microducts | 12–432 | FTTH, metro | — |
| Drop cable (FTTH) | 1–4 G.657 fibres, flat, self-supporting or indoor | 1–4 | last 50–500 m to the subscriber | bend-insensitive fibre |
| Trunk MPO (data centre) | 12/24/144 fibres pre-terminated with MPO connectors | 12–144 | leaf–spine, structured DC cabling | polarity method A/B/C (Breakout & MPO) |
Fibre and colour coding inside cables: 12 colours per TIA-598 (blue, orange, green, brown, slate, white, red, black, yellow, violet, rose, aqua), tubes colour-coded the same way (Labels & colour codes).
Termination: panels, pigtails, cassettes
| Component | What it does | Loss |
|---|---|---|
| Pigtail | 1–2 m of fibre with a factory connector on one end, bare on the other; fusion-spliced to the cable | connector 0.1–0.3 dB + splice 0.05 |
| Patch panel / ODF (optical distribution frame) | holds adapters (LC/SC duplex, MPO) where pigtails meet patch cords; splice trays behind | one mated pair per port |
| Splice cassette / tray | organises and protects splices with bend-radius control | — |
| Pre-terminated cassette | MPO trunk in, 12/24 LC ports out (fan-out inside) | 0.3–0.5 dB per path (MPO + LC pairs) |
| Field-installable connector | mechanical or fusion-spliced connector installed on site | 0.3–0.5 dB (mechanical), 0.1–0.2 (splice-on) |
| Wall outlet / terminal box | subscriber or work-area termination | one pair |
Design rule: every mated pair in the path counts — module to patch cord (1), patch cord to panel (2), panel to far patch cord (3), patch cord to module (4); cassettes add MPO pairs.
Splices
| Type | Loss (SMF) | Loss (MMF) | Return loss | Use |
|---|---|---|---|---|
| Fusion, single-fibre | 0.02–0.1 dB (typ. 0.03) | 0.05–0.2 | > 60 dB (no reflection) | all permanent joints |
| Fusion, ribbon (mass) | 0.05–0.15 dB | — | > 60 dB | high-count cables |
| Mechanical | 0.2–0.5 dB | 0.3–0.5 | 35–45 dB (index-matching gel) | temporary, restoration |
Splice loss is measured with an OTDR (bidirectional average); a splice reading > 0.3 dB is redone (Testing). Splicing G.652 to G.657 or to DSF adds 0.05–0.3 dB from mode-field mismatch (Light in fibre).
Connectors and adapters
Detail in Connectors & fibre types; the plant-side essentials:
| Item | Values |
|---|---|
| Insertion loss grades (IEC 61755) | grade A ≤ 0.07 dB (rare), B ≤ 0.12 (0.25 max), C ≤ 0.25 (0.5 max), D ≤ 0.5 (1.0 max) |
| Return loss | UPC ≥ 50 dB (grade 1), ≥ 45 (grade 2); APC ≥ 60 dB |
| Mating cycles | 500–1 000 before loss degrades |
| Adapter sleeves | zirconia ceramic (precision) vs phosphor bronze (cheap, wears); keep dust caps on empty adapters |
| MPO | male (pins) / female (no pins), key up/down, polarity A/B/C; low-loss ≤ 0.35 dB, standard ≤ 0.75 |
Attenuators
| Type | Range | Use |
|---|---|---|
| Fixed plug-in (bulkhead) | 1, 2, 3, 5, 7, 10, 15, 20 dB; ±0.5 dB; UPC or APC | protect receiver from overload on short links (Link budget) |
| Variable (VOA), mechanical | 0–30 dB, screw-adjusted | commissioning, lab |
| Variable, electronic (eVOA) | 0–20 dB, controlled | DWDM channel equalisation (DWDM components) |
| Air-gap vs doped-fibre | air-gap reflects (avoid on long links); doped-fibre absorbs | prefer absorptive for laser sources |
Attenuator wavelength dependence is small (±0.5 dB across 1310–1550) but not zero; specify the working wavelength.
Splitters (PON)
| Ratio | Insertion loss (typ. / max) | Note |
|---|---|---|
| 1:2 | 3.5 / 3.9 dB | — |
| 1:4 | 6.9 / 7.4 | — |
| 1:8 | 10.2 / 10.8 | — |
| 1:16 | 13.5 / 14.1 | — |
| 1:32 | 16.8 / 17.5 | GPON class B+ typical |
| 1:64 | 20.2 / 21.0 | class C+ / XGS-PON |
| 1:128 | 23.5 / 24.5 | rare; needs E-class budgets |
PLC (planar lightwave circuit) splitters are wavelength-flat 1260–1650 nm and uniform; FBT (fused biconic taper) splitters are cheaper, wavelength-dependent and used for 1:2/1:4 or unbalanced (e.g. 90/10 tap) ratios. Cascading 1:4 then 1:8 costs ~0.5 dB more than a single 1:32 (How PON works).
WDM filters and muxes
| Device | Loss | Isolation | Use |
|---|---|---|---|
| CWDM mux/demux 4/8/16-ch (TFF) | 1.0–2.5 dB per pass | 30 dB adjacent | CWDM |
| DWDM AWG 40/48/96-ch | 3–6 dB | 25–30 dB | DWDM |
| DWDM TFF 8-ch | 1.5–3 dB | 30 dB | small counts |
| OADM 1–4 ch | 1–2 dB drop, 0.8–1.5 dB pass | 30 dB | ring add/drop |
| BiDi / WDM coupler 1310/1550 | 0.5–1 dB | 20–30 dB | single-fibre working |
| PON WDM1r (1490/1310/1550 video overlay) | 0.5–1 dB | 30 dB | RF video overlay |
| Monitoring tap 1625/1650 nm | 0.3–0.5 dB | — | live OTDR |
Enclosures and environments
| Enclosure | Where | Concerns |
|---|---|---|
| Splice closure (dome / inline) | manholes, poles, direct burial | sealing (IP68), gel or mechanical seals, re-enterable |
| Street cabinet / FDH | FTTH distribution | splitters, temperature, humidity, security |
| Wall box / FAT | building entry | bend radius, slack storage |
| Rack ODF | equipment rooms | labelling, slack management, front/rear access |
| Rack cable management | data centres | bend radius ≥ 30 mm (SMF) / 10 × diameter, no tight ties, separate fibre from copper weight |
Design and handling rules
- Count every mated pair and splice; use design allowances, not typical values.
- Prefer fusion splices and factory-terminated pigtails; avoid mechanical splices in the permanent link.
- Bend radius: ≥ 30 mm for standard SMF cords in service (≥ 15 mm G.657.A1, ≥ 7.5 mm A2), ≥ 20 × cable diameter during installation.
- Dust caps on every open adapter and connector; clean before every mating (Connectors & fibre).
- Label both ends of every cord with the far-end position; record fibre numbers and colours in the plant database.
- Keep 3–5 m of slack in closures and 1–2 m in panels for future re-splicing.
- Separate APC (green) and UPC (blue) worlds; never mate them.
- Test after installation and keep the results (Testing).
In CodingBox
The plant fixes the loss and the wavelength; the module has to match both. CodingBox shows the module's connector code, wavelength and rated fibre lengths so a module is paired with the right plant — APC plant needs APC-compatible modules on the patch cord side, PON optics need the class the splitter budget demands (Check transceiver).
Making the joints in this plant — fusion and mechanical splicing, pigtails, field connectors, acceptance criteria: Splicing and termination; getting the cable there — ducts, direct burial, aerial, indoor pathways, bend and tension limits: Cable routes and installation.